The rate of release of amino acids during partial acid hydrolysis of bovine submaxillary mucin has been studied. A number of di‐ and tripeptides have been isolated on the amino acid analyzer. Three β‐hydroxyamino acid peptides, Thr‐Thr‐Thr, Ser‐Ser, and Thr‐Ser have been isolated and account for 12 % of these amino acids in native mucin. A substantial amount of the glycine and alanine has been isolated as dipeptides of serine and threonine with the fihydroxyamino acids in the amino‐terminal position. Proline, valine, isoleucine, and leucine seem to be in close association in the peptide core. The same pattern of peptides has been obtained from the partial acid hydrolysis of ovine subm